1. Field of the Invention
The present invention relates to a zoom lens device, comprising a total of four lens units, which is suitable for use in a single-lens reflex camera, a lens shutter camera, a video camera, or the like, and, more particularly, to a zoom lens device having a shooting angle of view of about 60 to 75 degrees at a wide angle end, and a magnification change-over ratio of about 2 to 3.5, wherein each lens unit is properly constructed in order to simplify the lens construction, properly correct aberrations, and decrease the overall length (measured from a surface of a first lens unit to an image plane) of the lens device.
2. Description of the Related Art
Recently, smaller single-lens reflex cameras, lens shutter cameras, video cameras, or the like have caused a demand for lighter photographic lenses having a shorter overall length.
For example, Japanese Patent Unexamined Publication Nos. 54-30855, 57-5012, 57-29024, 60-57814, 61-56315, 4-317019, 4-317020, and 4-321007 disclose zoom lens devices comprising three lens units in order to reduce the overall size of the lens system. The lens unit closest to an object side has a positive refractive power. The second closest lens unit has a negative refractive power. The lens unit furthest from the object side has a positive refractive power.
Japanese Patent Unexamined Publication Nos. 60-14213 and 60-14214 disclose zoom lens devices with a shooting angle of view of about 60 degrees at the wide angle end, and a magnification change-over ratio of about 3 to 6. The zoom lens device comprises four lens units, in which the lens unit closest to the object side has a positive refractive power, the next closest lens unit has a negative refractive power, the third closest lens unit has a positive refractive power, and the lens unit furthest from the object side has a positive refractive power.
Japanese Patent Unexamined Publication Nos. 62-247316 and 62-24213 disclose zoom lens devices comprising four lens units. They are in order of lens units from the lens closest to the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. Magnification changes are performed by moving the second lens unit, while variations in an image plane which occur as the magnification changes are corrected and focusing is performed by moving the fourth lens unit.
Japanese Patent Unexamined Publication No. 58-160913 discloses a zoom lens device comprising four lens units. They are in order of lens units from the lens unit closest to the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. Magnification changes are performed by moving the first and second lens units, while variations in an image plane which occur as the magnification changes are corrected by moving the fourth lens unit.
Japanese Patent Unexamined Publication No. 63-66522 discloses a zoom lens device comprising four lens units which are in order of lens units from the lens unit closest to the object, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. Magnification changes are performed by moving the first, the third, and the fourth lens units.
Japanese Patent Unexamined Publication No. 3-6507 discloses a zoom lens device comprising four lens units. The lens unit closest to the object side has a positive refractive power. The next closest lens unit has a negative refractive power. The third closest lens unit has a positive refractive power, and the lens unit furthest from the object side has a positive refractive power. Magnification changes are performed by individually moving each of the four lens units.
In general, in zoom lens devices, it is necessary to properly construct each of the lens units in order to reduce the overall size of the lens system, obtain a predetermined magnification change-over ratio, and achieve good optical performance over the entire magnification change-over range. In the zoom lens devices, increasing the refractive power of each lens unit reduces the amount of movement of each lens unit when magnification changes are being performed, thereby reducing the overall length of the lens system. However, merely increasing the refractive power of each lens increases aberration changes which occur as the magnification changes, thus making it difficult to properly correct the aberration changes.
In the zoom lens device proposed in the aforementioned Japanese Patent Unexamined Publication No. 60-57814, a stop is integrally moved with the second lens unit when the magnification is being changed from the wide angle end to the telephoto end, so that changes in the f-number tend to be large. In addition, it is difficult to use this type of zoom lens device as a replacement lens for a single-lens reflex camera, since the back focus is short.
Japanese Patent Unexamined Publication Nos. 60-142319, 61-56315, 1-223410, and 1-241513 disclose telephoto-type zoom lens devices which, however, cannot be used in ordinary shooting, since the focal length at the wide angle side tends to be too long. Even when these types of lenses are transformed into wider angle lenses, it is extremely difficult to correct aberrations and the required back focus cannot be obtained.
Japanese Patent Unexamined Publication Nos. 4-317019, 4-317020, and 4-321007 disclose zoom lens devices comprising basically three lens units so as to use fewer lenses. However, such lenses are not potentially capable as zoom lenses, thus making it necessary to form approximately more than half of the lens surfaces into aspherical surfaces, as a result of which it becomes difficult to manufacture the lenses and costs are increased.
Japanese Patent Unexamined Publication Nos. 60-14213, 62-24213, 63-66522, and 3-6507 disclose zoom lens devices comprising four lens units, which use a large number of lenses to form the overall lens system, and have a long overall length, thereby tending to increase the overall size of the lens system.